Ethylene polymer

ABSTRACT

An ethylene polymer excellent in molding processability represented by uniform extensibility, drawdown resistance, swell and extrudability, and mechanical properties represented by rigidity, impact resistance and ESCR, is provided. Particularly, an ethylene polymer remarkably excellent in balance between rigidity and ESCR as compared with a conventionally known ethylene polymer is provided.  
     An ethylene polymer, which is an ethylene homopolymer or a copolymer of ethylene with an α-olefin having a carbon number of from 3 to 20, and which satisfies the following conditions (1) to (4):  
     (1) the melt index (HLMI) under a load of 21.6 kg at 190° C. is from 0.1 to 1000 g/10 min,  
     (2) the density (d) is from 0.935 to 0.985 g/cm 3 ,  
     (3) the relation between HLMI and (d) satisfies the following formula (i):  
       d ≧0.00900 ×Log ( HLMI )+0.951  (i)  
     (4) the relation between ESCR and the flexural modulus (M) satisfies the following formula (ii):  
       M ≧−7310× Log ( ESCR )+32300  (ii)

TECHNICAL FIELD

[0001] The present invention relates to novel ethylene polymers. Moreparticularly, it relates to an ethylene polymer which is excellent inthe balance between mechanical characteristics, particularlyenvironmental stress cracking resistance (ESCR) and rigidity, andfurther, excellent in molding processability in e.g. extrusion, vacuummolding, film molding or blow molding, as compared with a conventionallyknown ethylene polymer.

BACKGROUND ART

[0002] In recent years, pipes and films made of plastics,injection-molded products and blow-molded products have been activelyused in various industrial fields. Particularly polyethylene type resinshave been used widely from such reasons as the low cost and lightweight, excellence in molding processability, chemical resistance andrecyclability.

[0003] In order to improve molding processability, since the molding iscarried out in a molten state of polyethylene, emphasis is put onimprovement in melt flow characteristics such as melt fluidity(easy-extrudability), melt extensibility and melt tension. For example,{circle over (1)} a method of broadening the molecular weightdistribution by a multistage polymerization method employing aconventional Ziegler catalyst or further incorporating a specificmolecular weight component (JP-A-2-53811, JP-A-2-132109,JP-A-10-182742), {circle over (2)} a method of using a traditional Crtype catalyst to produce a polyethylene having a long chain branching oradding a radical generator and a crosslinking aid to a resin tointroduce a long chain branching (JP-B-2-52654), {circle over (3)} amethod of using a polyethylene having a high melt extension stress toimprove uniform extensibility (JP-A-10-7726) and the like have beenproposed. However, there are many problems in the method {circle over(1)} such that the molded product tends to be more sticky or the impactstrength tends to decrease by increase of a low molecular weightcomponent, or gel is likely to form by increase of a high molecularweight body, there is such a problem in the method {circle over (2)}that the impact strength tends to decrease, and there is such a problemin the method {circle over (3)} that ESCR is not sufficient yet,although molding processability and impact strength are improved.

[0004] Further, in order to improve mechanical properties, {circle over(1)} a method of carrying out such a control that a low molecular weightcomponent alone is decreased while maintaining a broad molecular weightdistribution by improvement of the multistage polymerization or thecatalyst with respect to a conventional Ziegler catalyst product toimprove impact strength while maintaining molding processability(JP-A-7-90021), {circle over (2)} a method of introducing an α-olefininto a specific molecular weight component by multistage polymerizationto improve ESCR (JP-A-10-17619), {circle over (3)} a method of using ametallocene catalyst which was developed in recent years to improvemechanical properties (JP-A-8-59741, JP-A-11-60633) and the like havebeen proposed. However, even by these methods, no ethylene polymerhaving both excellent mechanical properties and molding processabilityat a high level has been obtained.

[0005] It is an object of the present invention to provide a novelethylene polymer excellent in molding processability represented byuniform extensibility, drawdown resistance and swell, and mechanicalproperties represented by rigidity, impact resistance and ESCR.

DISCLOSURE OF THE INVENTION

[0006] The present inventors have conducted extensive studies toovercome the above problems and as a result, found that an ethylenepolymer which is an ethylene homopolymer or a polymer of ethylene withanother α-olefin, wherein the melt index (HLMI) under a load of 21.6 kgand the density (d) are within specific ranges, and the relation betweenthem is within a specific range, is excellent in molding processabilityand mechanical characteristics. The present inventors have further foundthat the balance between rigidity represented by flexural modulus andESCR is unprecedentedly excellent, and the present invention has beenaccomplished on the basis of these discoveries.

[0007] Namely, the present invention provides an ethylene polymer, whichis an ethylene homopolymer or a copolymer of ethylene with an α-olefinhaving a carbon number of from 3 to 20, and which satisfies thefollowing conditions (1) to (4):

[0008] (1) the melt index (HLMI) under a load of 21.6 kg at 190° C. isfrom 0.1 to 1000 g/10 min,

[0009] (2) the density (d) is from 0.935 to 0.985 g/cm³,

[0010] (3) the relation between HLMI and d satisfies the followingformula (i):

d≧0.00900×Log(HLMI)+0.951  (i)

[0011] (4) the relation between ESCR and the flexural modulus (M)satisfies the following formula (ii):

M≧−7310×Log(ESCR)+32300  (ii)

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1: GPC curves of ethylene polymers obtained in Examples 1 to4

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] Now, the mode of carrying out the present invention will beexplained below.

[0014] The ethylene polymer of the present invention is an ethylenehomopolymer or a copolymer of ethylene with an α-olefin having a carbonnumber of from 3 to 20. The α-olefin as a comonomer used may, forexample, be propylene, butene-1, 3-methylbutene-1, 3-methylpentene-1,4-methylpentene-1, hexene-1, octene-1, pentene-1, decene1,tetradecene-1, hexadecene-1, octadecene-1 or eicosene1. Further, a vinylcompound such as vinyl cyclohexane or styrene or its derivative may alsobe used. Such an α-olefin may be used alone or as a combination of atleast two types. Among them, more preferred as the α-olefin is onehaving a carbon number of from 3 to 10 such as propylene, butene-1 orhexene-1. The ethylene polymer of the present invention is preferably anethylene homopolymer. The ethylene homopolymer is a polymer produced bysupplying ethylene alone as a monomer material to a reactor.

[0015] The proportion of ethylene and α-olefin in the aboveethylene/α-olefin copolymer is preferably such that ethylene is from 90to 100 wt % and α-olefin is from 0 to 10 wt %, more preferably ethyleneis from 95 to 100 wt % and α-olefin is from 0 to 5 wt %. If the α-olefincontent is higher than the above range, the rigidity of the ethylenepolymer tends to decrease, such being unfavorable.

[0016] The ethylene polymer of the represent invention is characterizedby satisfying the following conditions (1) to (4) as physical propertiesof the polymer.

[0017] [Physical Properties]

[0018] (1) Melt Index (HLMI)

[0019] The ethylene polymer of the present invention has a melt index(HLMI; unit: g/10 min) under a load of 21.6 kg at 190° C. of from 0.1 to1000. If HLMI is less than 0.1, the extrudability tends to be poor, andsurface roughing may occur at the time of parison formation in a case ofblow molding, breaking by blowing may occur in a blow-up step, suchbeing unfavorable, and if it exceeds 1000 drawdown tends tosignificantly occur, or the impact resistance tends to decrease, suchbeing unfavorable. HLMI is preferably within a range of from 0.5 to 100.HLMI is more preferably within a range of from 1.0 to 100. HLMI is mostpreferably within a range of from 1.0 to 50.

[0020] Measurement of HLMI

[0021] It means one measured under a load of 21.6 kg at 190° C. inaccordance with ASTM-D-1238-57T. Usually the melt index is measuredunder a load of 2.16 kg, however, the range of the melt index of theethylene polymer of the present invention is from the limit ofmeasurement or below (usually <0.01, i.e. the amount of flow in 10minutes is less than 10 mg) to a level of 30, and accordingly, it isnecessary to measure the value under a ten-time load so as to minimizethe measurement error. An abbreviated expression of HLMI is employed ina sense of melt index under a high load.

[0022] In the condition (1), in order to control HLMI to a desiredvalue, a method of increasing HLMI by making a chain transfer agent suchas hydrogen in a proper amount as a molecular weight modifier be presentin the polymerization system, a method of increasing HLMI by increasingthe polymerization temperature, may, for example, be mentioned.

[0023] (2) Density (d)

[0024] The ethylene polymer of the present invention has a density (d)of from 0.935 to 0.985 (g/cm³). If the density is less than 0.935, therigidity tends to be low, such being unfavorable. Further, if thedensity is higher than 0.985, the impact resistance tends to decrease orESCR tends to decrease, such being unfavorable. The above density ispreferably from 0.945 to 0.980, more preferably from 0.950 to 0.975.

[0025] Measurement of Density

[0026] It is one measured by a density gradient tube method inaccordance with JIS-K6760. For measuring the density, the ethylenepolymer is subjected to press molding at a temperature of 190° C. toobtain a pressed sheet, which is subjected to annealing at a temperatureof 100° C. for 1 hour, followed by cooling to room temperature at a rateof about 20° C./hr to obtain a sample, and the sample thus obtained isused.

[0027] In the condition (2), in order to control the density to adesired value, a method of copolymerizing the above-mentioned α-olefinor the like with ethylene to decrease the crystallinity thereby tocontrol the density to a desired value, a method of decreasing the meltindex to decrease the crystallinity thereby to decrease the density, amethod of introducing a component having a high molecular weight tosuppress progress of crystallization thereby to decrease thecrystallinity and to decrease the density, may, for example, beemployed.

[0028] (3) Relation Between Melt Index (HLMI) and Density (d)

[0029] Of the ethylene polymer of the present invention, the relationbetween HLMI and (d) satisfies the formula (i):

d≧0.00900×Log(HLMI)+0.951  (i)

[0030] In the formula (i), Log represents a common logarithm. It isknown that with respect to the ethylene polymer, the higher themolecular weight, i.e. the smaller HLMI, the more the density decreasesin general. Further, “Creation of new generation highly functionalpolymers and recent catalyst technology” (edited by Minoru Terano,published by Gijyutsu Kyoiku Shuppan, Limited, publication data: May2001) on page 128 discloses that “no high density polymer can beproduced with a conventional m-PE, which can be produced with ZN-PE”.However, the present inventors have succeeded in producing an ethylenecopolymer having a higher density as compared with a conventionallyknown ethylene polymer in comparison at the same HLMI, by employing aspecific metallocene catalyst and/or by employing a specificpolymerization method to design a characteristic molecular weightdistribution structure. The ethylene polymer of the present invention isgreatly characterized by satisfying the formula (i) and in such a case,excellent mechanical properties will be obtained.

[0031] In the condition (3), in order that the relation between thedensity and HLMI satisfies the formula (i), physical properties whichare inconsistent with a conventionally known correlation between HLMIand the density have to be satisfied simultaneously, which can beaccomplished in the present invention by making a component having anadequately high melt viscosity to maintain a low HLMI value and anadequately highly crystalline component to maintain a high density valuebe present in predetermined proportions in the ethylene polymer of thepresent invention. By changing their proportions, the density and HLMIcan be controlled within a range where the formula (i) is satisfied. Thevalues of HLMI, the density, the flexural modulus and ESCR also change,and accordingly it is required to change their proportions within arange where the conditions (1) and (2) and the formula (ii) aresatisfied.

[0032] In a case where the relation of the formula (i) is not satisfied,the rigidity may decrease, the impact resistance may decrease, ESCR maydecrease or the creep characteristics may be poor, such beingunfavorable. Excellent mechanical properties will be obtained when therelation between HLMI and the density satisfies the formula (i-l), morepreferably when it satisfies the formula (i-2):

d≧0.00697×Log(HLMI)+0.956  (i-1)

d≧0.00697×Log(HLMI)+0.957  (i-2)

[0033] (4) Relation Between Environmental Stress Cracking Resistance(ESCR) and Flexural Modulus (M)

[0034] In general, the flexural modulus (M) and the common logarithm Log(ESCR) of the environmental stress cracking resistance are in inversecorrelation. The ethylene polymer of the preset invention realizes bothflexural modulus and ESCR at a high level which have conventionally beenimpossible to achieve, and satisfies the relation of the formula (ii):

M≧−7310×Log(ESCR)+32300  (ii)

[0035] When copolymerization with an α-olefin is carried out with apurpose of improving mechanical strength of the molded product such asimpact resistance and ESCR, conventionally the density of the copolymeris set to be relatively low, whereby there is such a drawback that theflexural modulus (rigidity) tends to decrease. Particularly in order tomake the product light and thin, the decrease in rigidity may causedeformation such as distortion, or the decrease in the melting pointmakes the product be likely to undergo heat deformation, such being inan inadequate condition.

[0036] The ethylene polymer of the present invention which satisfies therelation of the formula (ii) has an extremely high rigidity. Thus, whenit is used for a molded product such as a large container or a pipe,deformation such as distortion is less likely to occur, it is possibleto make the product thin as compared with a conventional one, andfurther, it has a high ESCR and it is thereby excellent in chemicalresistance and weather resistance, such being extremely effective inpractical use.

[0037] In the condition (4), in order that the relation between theflexural modulus (M) and the environmental stress cracking resistance(ESCR) satisfies the formula (ii), it can be achieved by controlling theamount of the highly crystalline component and the number of so-calledtie molecules, because the amount of the highly crystalline componentaffects the value of the flexural modulus, and the tie molecules affectthe strength of the amorphous part. A tie molecule is a molecule whichis present on both one crystal lamella and another crystal lamella.Generally, a component having a higher molecular weight is more likelyto be a tie molecule. The values of HLMI and the density also change,and accordingly it is necessary to carry out the change within a rangewhere the conditions (1) and (2) and the formula (i) are satisfied.

[0038] When the relation of the formula (ii) is not satisfied,mechanical properties tend to decrease, such being unfavorable. Anethylene polymer having a flexural modulus of at least 15000 kgf/cm2 isextremely useful for all applications. An ethylene polymer having ESCRof at least 500 hours is extremely useful for applications in whichchemical resistance and light resistance are particularly required. Itis more preferred that the relation between the flexural modulus andESCR satisfies the formula (ii-1), furthermore preferably it satisfiesthe formula (ii-2). Most preferably, it satisfies the formula (ii-3):

M≧−7310×Log(ESCR)+34000  (ii-1)

M≧−7310×Log(ESCR)+35300  (ii-2)

M≧−7310×Log(ESCR)+37000  (ii-3)

[0039] Measurement of ESCR

[0040] It is measured at 50° C. in accordance with JIS-K6760. As asurfactant, a 10 wt % aqueous solution of LIPONOX NC (trade name,manufactured by LION CORPORATION) is used. The notch depth is 0.3 mm.

[0041] Measurement of Flexural Modulus

[0042] It is carried out by means of a three point bending method inaccordance with JIS-K7203. The specification and the molding method ofthe test piece used, and the test conditions are as follows.

[0043] [Specification of Test Piece]

[0044] Length: at least 80 mm

[0045] Width: 25±0.5 mm

[0046] Thickness: 2±0.2 mm

[0047] [Molding Method of Test Piece]

[0048] A pressed sheet is molded from pellets in accordance with thefollowing (1) to (5).

[0049] (1) Standing in a pressing machine at 170±5° C. for 5 minutes

[0050] (2) Deaeration for 20 seconds

[0051] (3) Pressurizing for 1 minute (60 kgf/cm² (588N/cm²))

[0052] (4) Pressurizing by a pressing machine at 100±2° C. for 5 minutes(60 kgf/cm² (588N/cm²))

[0053] (5) Pressurizing by a pressing machine at 30±2° C. for 5 minutes(60 kgf/cm² (588N/cm²))

[0054] [Test Conditions]

[0055] Distance between supporting points: 35.0 mm

[0056] Testing rate: 1.0 mm/min

[0057] Support radius: 2±0.2 mm

[0058] The load is measured when the bending amount is 2.0 mm.

[0059] In order that the above physical properties of the ethylenepolymer of the present invention are achieved, the following condition(5) is preferably satisfied in addition to the above conditions (1) to(4).

[0060] (5) The Relation Between the Molecular Weight (Mlmax) at theHighest Peak Position in the Molecular Weight Distribution Curve asMeasured by Gel Permeation Chromatography (GPC) and the Melt Index Undera High Load (HLMI) Satisfies the Formula (iii)

Log(M1max)≦−0.307×Log(HLMI)+4.87  (iii)

[0061] In the formula (iii), Log represents a common logarithm. Ingeneral, GPC is a simple measuring method with relatively high accuracyfor measuring the molecular weight distribution of a polymer containingcomponents having a molecular weight of from about several hundreds toabout several million. On the other hand, HLMI is measured under a highload, and is one of measuring methods by which fluidity of a polymer atthe time of melting can be known most simply, even if the polymercontains a considerable amount of components having a molecular weightexceeding a million i.e. so-called ultrahigh molecular weightcomponents.

[0062] M1max represents a molecular weight with the highest proportionin the molecular weight distribution of the polymer as measured by GPC,and is an index which controls polymer physical properties regarding themolecular weight. The ethylene polymer of the present inventionpreferably has at least two components of a main peak component with anarrow molecular weight distribution having a highest peak position atthe low molecular weight side of at most 200,000, preferably at most50,000, furthermore preferably at most 20,000, most preferably less than10,000, and a high molecular weight component with a broad peak whichcovers the high molecular weight side exceeding 1,000,000, preferably2,000,000, more preferably 3,000,000, most preferably 4,000,000, in themolecular weight distribution curve as obtained by GPC measurement,whereby not only the polymer is excellent in mechanical properties butalso its molding processability improves. Further, when the relation ofthe formula (iii) is satisfied, improvement in melt fluidity(easy-extrudability) due to contribution by the main peak componenthaving a low molecular weight with a narrow molecular weightdistribution represented by Mlmax and improvement in mechanicalproperties such as impact resistance due to contribution by the highmolecular weight component represented by HLMI, are simultaneouslyrealized. On the other hand, if the relation of the formula (iii) is notsatisfied, the melt fluidity tends to deteriorate or mechanical strengthsuch as impact resistance tends to deteriorate in some cases.

[0063] By using the value as defined hereinafter which simply representsthe degree of narrowness of the molecular weight distribution of themain peak component with a narrow molecular weight distribution on thelow molecular weight side, the characteristics of the ethylene polymerof the present invention can be defined more clearly. Namely, when themolecular weight at the point where a line which passes a point whichdivides a perpendicular drawn from the main peak position of the GPCcurve to the base line in half, and which is parallel to the base line,and the GPC curve intersect with each other at the low molecular weightside, is M1/2, the ratio of M1/2 to Mlmax is at least 0.10, preferablyat least 0.20, more preferably at least 0.30, most preferably at least0.35.

[0064] In the condition (5), in order that the relation between Mlmaxand HLMI satisfies the formula (iii), it is required that the maincomponent consisting of the low molecular weight polymer with a lowmolecular weight distribution and the above-described component havingan adequately high melt viscosity to maintain a low HLMI value, arecontained in an appropriate mixture ratio in the ethylene polymer tooptimize the molecular weight distribution. The values of HLMI, thedensity, the flexural modulus and ESCR also change, and accordingly itis required to carry out the change within a range where the conditions(1) and (2), the formula (i) and the formula (ii) are satisfied.

[0065] Here, although Mlmax of the polymer is low as compared with theconventional ethylene polymer, it shows a low HLMI. As mentioned above,the ethylene polymer of the present invention has a broad molecularweight distribution with a low molecular weight component and a highmolecular weight component, and the Q value (Mw/Mn) which is the ratioof the weight average molecular weight (Mw) and the number averagemolecular weight (Mn) as obtained by GPC measurement which is commonlyemployed as a measure of the width of the molecular weight distribution,is preferably higher than 7, more preferably higher than 14, furthermorepreferably higher than 17.

[0066] The relation between the molecular weight (M1max) at the highestpeak position in the molecular weight distribution curve as measured byGPC and HLMI of the ethylene polymer of the present invention morepreferably satisfies the formula (iii-l), most preferably it satisfiesthe formula (iii-2):

Log(M1max)≦−0.307×Log(HLMI)+4.60  (iii-1)

Log(M1max)≦−0.307×Log(HLMI)+4.50  (iii-2)

[0067] The lower limit of Mlmax is 1000, preferably 2000, morepreferably 3000. If Mlmax is lower than the above lower limit, theamount of a low molecular weight polymer tends to increase, whereby theimpact resistance tends to decrease, smoking at the time of molding orstain in the molding machine tends to be significant, or the surface ofthe product tends to be sticky, thus impairing the taste or smell whenused as a food container, such being unfavorable.

[0068] Molecular Weight Measurement by GPC

[0069] Mw/Mn is obtained as calculated as Mw and Mn by means of auniversal method, using the standard polystyrene of which the molecularweight is known. For measurement, IOSC-ALC/GPC manufactured by WatersK.K. is employed, three AD80-M/S manufactured by SHOWA DENKO K.K. areemployed as columns, a sample is dissolved in o-dichlorobenzene toobtain a 0.2 wt % solution and 200 μm thereof is used, and measurementis carried out at 140° C. at a flow rate of 1 ml/min.

[0070] In order that the above physical properties of the ethylenepolymer of the present invention are achieved, the following condition(6) is preferably satisfied in addition to the above conditions (1) to(5).

[0071] (6) Relation Between the Melting Point (Tm) as Obtained byDifferential Scanning Calorimetry (DSC) Measurement and the Density (d)Satisfies the Formula (iv)

Tm≦538d−378  (iv)

[0072] The melting point (Tm) as obtained by DSC measurement in thepresent invention means the main peak temperature (° C.) in theendothermic curve. The ethylene polymer of the present invention has alow melting point as compared with a conventionally known ethylenepolymer having the same density, and when the relation of the formula(iv) is satisfied, it is excellent in fusing properties at the time ofmolding and mechanical strength of the molded product, particularly itis very excellent in balance between the flexural modulus (rigidity) andESCR. This is estimated to be due to the fact that the ethylene polymerof the present invention contains a component which has extremely highcrystallization speed and fusion speed.

[0073] Of the ethylene polymer of the present invention, the relationbetween Tm and d more preferably satisfies the formula (iv-l), mostpreferably the formula (iv-2):

Tm≦538d−379  (iv-1)

Tm≦538d−380  (iv-2)

[0074] Further, as one of preferred conditions of the ethylene polymerof the present invention to prevent thermal deformation of products (toimprove heat resistance), the relation between Tm and d satisfies theformula (v):

Tm≧400d−250  (v)

[0075] The relation between the melting point (Tm) as obtained by DSCmeasurement and the heat quantity of fusion (AH) of the ethylene polymerof the present invention satisfying the formula (vi) may be mentioned asone of preferred conditions. The unit of the heat quantity of fusion isJ/g.

ΔH≧5.47Tm−528  (vi)

[0076] In the condition (6), in order that the relation between themelting point Tm and the density (d) satisfies the formula (iv), themolecular weight distribution and the copolymer composition distributionof the ethylene polymer are optimized to control the crystallinitydistribution. Specifically, it can be achieved by controlling thecontent of a polymer component with a low comonomer content having a lowmolecular weight as a highly crystalline component.

[0077] Melting Point Measurement by DSC

[0078] It is carried out in accordance with JIS-K7121.9 mg of a sampleis melted at 160° C. for 10 minutes, the temperature is lowered to 40°C. at a rate of 10° C./min, the sample is held for 2 minutes, and then afusion curve is measured up to 160° C. at a temperature-raising rate of10° C./min, and the peak top temperature (° C.) is taken as the meltingpoint (Tm).

[0079] Measurement of Heat Quantity of Fusion by DSC

[0080] It is calculated in accordance with JIS-K7122 and is representedby the unit J/g.

[0081] In order that the above physical properties of the ethylenepolymer of the present invention are achieved, it is preferred that thefollowing condition (7) is satisfied in addition to the above conditions(1) to (6).

[0082] (7) The Weight Percentage (Mc Value) of a Component Having aMolecular Weight of at Least 1,000,000 as Obtained from GPC-MallsMeasurement is at Least 5%

[0083] If the Mc value is low, uniform extensibility or drawdownresistance at the time of blow molding tends to deteriorate, or theimpact resistance strength tends to decrease, such being unfavorable.The range of the Mc value is more preferably at least 7%, particularlypreferably at least 10%.

[0084] A so-called ultrahigh molecular weight component having amolecular weight of at least 1,000,000 has a large inertia radius ofmolecules in a molten state, and has an extremely low mobility, wherebyit is likely to be incorporated into between different crystal lamellaein the process of crystallization. Namely, it is likely to be present inthe polyethylene solid as a tie molecule. Accordingly, an ethylenepolymer having a high Mc value which represents the weight percentage ofa ultrahigh molecular weight component is likely to form a polyethylenesolid with a large number of tie molecules, and as a result, it tends tohave excellent mechanical properties such as improved impact resistanceand improved ESCR.

[0085] The above Malls measurement is an abbreviation for multi anglelaser light scattering. The upper limit of the Mc value is notparticularly limited, however, if it is too high, the melt fluiditytends to be poor, and accordingly it is preferably 30%, more preferably25%, furthermore preferably 20%.

[0086] In the condition (7), in order that the Mc value is within theabove range, an operation to increase the proportion of the ultrahighmolecular weight component in the ethylene polymer is carried out. Atthis time, the value of HLMI also changes, and accordingly it isrequired to change the proportion within a range where the formulae (i)and (iii) are satisfied.

[0087] GPC-Malls Measurement and Definition of Mc Value

[0088] It is obtained by subjecting data obtained by the measuringapparatus under conditions by calibration as mentioned in (1) to dataprocessing as mentioned in (2).

[0089] (1) Data Measurement

[0090] [Apparatus]

[0091] GPC: 150 CV (including RI detector) manufactured by Waters K.K.

[0092] Malls: DAWN•DSP (flow cell: F2 cell) manufactured by Wyatt.

[0093] (Data processing soft: ASTRA Version 4.50 manufactured by Wyatt)

[0094] [Conditions]

[0095] Column: Shodex UT-806M (two columns) manufactured by SHOWA DENKOK.K.

[0096] Solvent: 1,2,4-trichlorobenzene containing 0.2 w/v % BHT (WakoPure Chemicals Industries, Ltd., HPLC grade)

[0097] Flow rate: 0.5 ml/min (as corrected as elution volume of BHT inthe measurement sample in practice)

[0098] Measurement temperature: 140° C. (injection part, column part,detector (RI and DAWN) part)

[0099] Injection amount: 0.3 ml

[0100] Sample concentration: 2 mg/ml

[0101] Sample preparation: A sample solution is heated for dissolutionin an air bath set at 140° C. for from 3 to 5 hours.

[0102] [Calibration]

[0103] NIST•SRM-1483 is employed as an isotropic scattering substancefor sensitivity correction of each detector of the Malls.

[0104] The delay volume between the Malls and the RI detector ismeasured by using the standard polystyrene (FlO) manufactured by TOSOHCORPORATION.

[0105] As the refractive index of the solvent and the Rayleigh ratio,1.502 and 3.570×10⁻⁵ are employed, respectively.

[0106] (2) Calculation of Mc Value

[0107] In a chromatogram employing a Rayleigh ratio having a scatteringangle extrapolated to 00, as obtained from the above measured data, thearea percentage (Mc value) (%) of a component having a molecular weightof at least 1,000,000 of the chromatogram is obtained from the followingcalculation.

[0108] The all area detected as peaks in the chromatogram of 900scattering of the Malls is designated as the calculation object, and themolecular weight is calculated by employing a data processing softASTRA. As the calculation method, injection weight, dn/dc (-0.104 ml/g)and Zimm plot (first approximation) are employed. The Rayleigh ratioR(0)_(i) having a scattering angle of each eluted component separated byGPC extrapolated to 0° is calculated from the following formula (1):

R(0)_(i) =K×ci×Mi  (1)

[0109] wherein c_(i) and M_(i) are the concentration and the molecularweight of the eluted component i obtained by calculation by employingthe data processing soft ASTRA,

[0110] respectively, and K is the optical constant calculated by theformula (2):

K={4π×n×(dn/dc)²}/{λ⁴ /NA}  (2)

[0111] π: circular constant=3.141

[0112] n: refractive index under the measurement condition of thesolvent=1.502

[0113] dn/dc: refractive index concentration increment under themeasurement condition of the sample=−0.104 (ml/g)

[0114] λ: wavelength of the light source in a vacuum =632.8×10⁻⁷ (cm)

[0115] NA: Avogadro's number=6.022×10²³ (/mol),

[0116] whereby K=9.976×10⁻⁸ (cm².mol/g²).

[0117] On the other hand, the elution volume V (1M) at a molecularweight of 1,000,000 is read from the relational line of the molecularweight of each eluted component as obtained from the above-describedZimm plot and the elution volume, and the area percentage of the highmolecular weight component of at least V (1M) in the chromatogram of theelution volume and R(0)i is calculated.

[0118] Molding Processability

[0119] The application in which characteristics of the ethylene polymerof the present invention having excellent mechanical propertiesrepresented by rigidity, impact resistance and ESCR which have notconventionally been achieved, are most remarkably obtained, may, forexample, be injection-molded products such as various pipes for gas andfor water supply and the like, films, and food goods and miscellaneousdaily goods, rotational-molded products, compressive injection-moldedproducts, extrusion-molded products, blow-molded products of varioussizes, including small containers used for e.g. food oil, detergents andcosmetics, medium size containers for industrial chemical cans and coaloil cans, and large containers such as metal drums and fuel tanks forautomobiles, and blow-molded products. In recent years, from theviewpoint of resource saving, labor saving and cost saving, requirementof furthermore weight saving and complicated shape of polyethyleneproducts are increasing. In order to meet such requirements, excellentmolding processability and forming properties are required as well asexcellent mechanical properties.

[0120] As the molding of a polyethylene resin is usually carried out ina molten state of the resin, various behaviors in a molten state areimportant. Various behaviors of the ethylene polymer of the presentinvention in a molten state are extremely characteristic and as aresult, the ethylene polymer which satisfies the above-describedphysical property definition has not only mechanical properties but alsoexcellent moldability. The moldability is superior when at least one ofthe following conditions (8) to (13) is satisfied.

[0121] (8) Melt Elongation Ratio (R)

[0122] The ethylene polymer of the present invention preferably has amelt elongation ratio (R) of at least 3.5, which represents the limit ofdeformation speed at which elongating is possible without rupture whenelongating deformation is applied in a molten state.

[0123] In the condition (8), in order that that R satisfies the aboverange, the molecular weight distribution and the degree of long chainbranching are controlled to optimize the viscoelastic behaviors.

[0124] An ethylene polymer is molded usually in a molten state.Particularly when molding with a melt elongating (extension) step suchas blow molding or film molding (blown-film molding) is carried out, itis important to prevent rupture or breaking by blowing in the elongatingstep, and the limit of the deformation speed at which elongating ispossible has to be high, that is, R has to be high.

[0125] The ethylene polymer of the present invention is greatlycharacterized by having a high R as compared with a conventionally knownethylene polymer, and when R is at least 3.5, excellent moldingprocessability will be obtained. If R is less than 3.5, rupture orbreaking by blowing tends to occur in the step of melt elongating, suchbeing unfavorable. More particularly, as R is dependent on molecularweight, it is preferred that:

[0126] (a) R satisfies the following formula (vii) when HLMI<8.0:

R≧−63.1×Log(HLMI)+62.7  (vii)

[0127] (b) R is at least 5.7 when HLMI≧−8.0.

[0128] Measurement of R

[0129] By using capirograph manufactured by Toyo Seiki Seisaku-Sho,Ltd., a measurement sample is extruded from an orifice with a nozzlesize of 1.0 mmφ, a nozzle length of 10 mm and an inlet angle of 900 at atemperature of 190° C. (extrusion linear velocity (V0): 1.82 m/min), andthe molten strand is subjected to a draw test at a draw rate (V). V is1.3 m/min at the beginning, and then it is increased at a rate of 40m/min, and V when the molten strand is ruptured is taken as Vk, and theratio of Vk to VO i.e. Vk/V0 is taken as the melt elongation ratio R.

[0130] (9) Relation Between the Melt Drawdown Index (Lm) and HLMI

[0131] Of the ethylene polymer of the present invention, the relationbetween HLMI and the melt drawdown index (Lm) which represents the drawratio when a load is applied to the molten strand extruded from anorifice and the strand is left to stand for a certain time, satisfiesthe following formula (viii):

Lm≦0.238×Log(HLMI)+1.32  (viii)

[0132] The lower limit of Lm is 0.950, preferably 0.980, more preferably1.00.

[0133] In a case where the ethylene polymer is subjected to blow moldingor extrusion, sagging (drawdown) due to its own weight and deformationoccurs on the molten resin in a state extruded from the molding die,thus impairing the thickness and shape of the molded product.Particularly in the field of blow molding for large products such asfuel containers such as plastic fuel tanks for automobiles and metaldrums, the weight of the molding precursor (parison) before blow-upreaches from several kg to several tens kg, and accordingly the saggingdue to its own weight has to be particularly small (that is, thedrawdown resistance has to be excellent).

[0134] Measurement of Lm

[0135] One having a laser scanning swell measuring apparatus mounted oncapirograph manufactured by Toyo Seiki Seisaku-Sho, Ltd. is employed. Ameasurement sample which is preheated at a temperature of 230° C. for 15minutes after packing is extruded from an orifice with a nozzle size of2.78 mmp, a nozzle length of 80 mm and an inlet angle of 3.740 at a rodrate of 15 mm/min. To the section with an initial length (L0) below thedie of 30 mm of the molten strand, a load of 8 KPa is applied. Thelength L (mm) at the time of t=30 seconds, at the section where L0=30 mmat the time of t=0 second, is measured, where the time at the beginningof application of the load is t (sec)=0. The ratio of L to LO, i.e. therate of elongation L/L0 is defined as the melt drawdown index Lm.

[0136] In the condition (9), in order that the relation between Lm andHLMI satisfies the formula (viii), the molecular weight distribution andthe degree of long chain branching are controlled to optimize theviscoelastic behaviors.

[0137] (10) Relation Between the Melt Elongation ratio (R) and the MeltTension (MT)

[0138] Of the ethylene polymer of the present invention, the relationbetween the R value under the above condition (8) and the melt tension(MT) measured at 190° C. preferably satisfies the following formula(ix), whereby more excellent molding characteristics will be obtained:

R≧35.5×Log(MT)−22.2  (ix)

[0139] Measurement of MT

[0140] By using a melt tension tester manufactured by Toyo SeikiSeisaku-Sho, Ltd., measurement is carried out under conditions of anozzle size of 1.0 mmφ, a nozzle length of 5 mm, an inlet angle of 900,at a temperature of 190° C., at an extrusion rate of 0.44 g/min, at adraw rate of 0.94 m/min, with a distance of 40 cm from the die outlet tothe V pulley lower end of the tension detector. The draft ratio (drawrate/nozzle linear velocity) is 1.25.

[0141] In the condition (10), in order that the relation between R andMT satisfies the formula (ix), the molecular weight distribution and thedegree of long chain branching are controlled to optimize theviscoelastic behaviors.

[0142] (11) Swell Ratio

[0143] The swell ratio is preferably at most 1.8, whereby significantswell of the molten resin extruded from a die at the time of molding canbe prevented, whereby it will not be difficult to control the size ofthe product. If the swell ratio is higher than 1.8, it will be necessaryto control a special die gap, or no product having the dimensioncontrolled with high accuracy will be obtained, such being unfavorable.The swell ratio is more preferably at most 1.6, furthermore preferablyat most 1.5. The lower limit is 1.0.

[0144] Measurement of Swell Ratio

[0145] The ratio of the strand outer diameter to the nozzle size when ameasurement sample is extruded from an orifice with a nozzle size of 1.0mmφ, a nozzle length of 10 mm and an inlet angle of 900 at a temperatureof 190° C. at an extrusion linear velocity (V0) of 1.82 m/min, usingcapirograph manufactured by Toyo Seiki Seisaku-Sho, Ltd., is taken asthe swell ratio.

[0146] In the condition (11), in order that the swell ratio is withinthe above range, the molecular weight distribution and the degree oflong chain branching are controlled to optimize the viscoelasticbehaviors.

[0147] The above-described excellent properties regarding themoldability are considered to be explained by the specific meltviscoelastic behaviors as represented by G′ and η as describedhereinafter.

[0148] (12) Storage Modulus (G's)

[0149] Of the ethylene polymer of the present invention, the relationsof the storage modulus [G's (ω=0.1)] (unit Pa) with a short frequency(ω) of 0.1 rad/sec and the storage modulus [G's (ω=1.0)] (unit: Pa) witha long frequency (ω) of 1.0 rad/sec, at 190° C., and HLMI, satisfy thefollowing formulae (x) and (xi), respectively:

Log[G's(ω=0.1)]≧−0.374×Log(HLMI)+4.35  (x)

Log[G's(ω=1.0)]≧−0.135×Log(HLMI)+4.62  (xi)

[0150] An ethylene polymer is molded usually in a molten state.Particularly when molding with a melt elongating (extension) step suchas blow molding or film molding (blown-film molding) is carried out, itis important to prevent rapture or breaking by blowing in the elongatingstep, and the limit of the deformation speed at which elongating ispossible has to be high.

[0151] The ethylene polymer of the present invention is characterized byhaving high G's (ω=0.1) and G's (ω=1.0) which satisfy the formulae (x)and (xi) as compared with a conventionally known ethylene polymer, andis excellent in melt elongating property and molding processability asrepresented by drawdown resistance and swell. If G's (ω=0.1) or G's(ω=1.0) does not satisfy the above range, rupture or breaking by blowingmay occur in the melt elongating step, or the drawdown at the time ofmolding tends to be significant, whereby it tends to be difficult tocontrol the shape of the product after blow-up, or the swell tends to besignificant, whereby it will be necessary to control a special die gap,or no product having the dimension controlled with high accuracy will beobtained, such being unfavorable.

[0152] In order to make the product thin with a purpose of weight savingor in order to impart a complicated shape, G's (ω=0.1) and G's (ω=1.0)more preferably satisfy the following formulae (x-1) and (xi-1),respectively:

Log[G's(ω=0.1)]≧−0.374×Log(HLMI)+4.43  (x-1)

Log[G's(ω=1.0)]≧−0.135×Log(HLMI)+4.69  (xi-1)

[0153] Furthermore preferably, they satisfy the following formulae (x-2)and (xi-2), respectively:

Log[G's(ω=0.1)]≧−0.374×Log(HLMI)+4.56  (x-2)

Log[G's(ω=1.0)]≧−0.135×Log(HLMI)+4.74  (xi-2)

[0154] Further, G's (ω=10) preferably satisfies the following formula,whereby the ethylene polymer will be excellent in prevention of ruptureor breaking by blowing in the elongating step or is excellent indrawdown resistance at the time of molding in some cases:

Log[G's(ω=10)]≧−0.309×Log(HLMI)+5.25

[0155] The upper limits of G's (ω=0.1), G's (ω=1.0) and G's (ω=10) arenot particularly limited, however, if they are too high, the meltelasticity tends to be too high, thus impairing the moldingprocessability, and accordingly they are preferably 0.1 MPa, 0.2 MPa and0.3 MPa, respectively, more preferably 0.07 MPa, 0.15 MPa and 0.2 MPa,respectively, furthermore preferably 0.05 MPa, 0.12 MPa and 0.17 MPa,respectively.

[0156] In the condition (12), in order that the relations between thestorage moduli G′ and HLMI satisfy the formulae (x) and (xi), themolecular weight distribution and the degree of long chain branching arecontrolled.

[0157] Measurement of Storage Modulus G's

[0158] As a stress-detecting type rotational viscometer, RMS-800manufactured by Rheometrics is employed. Measurement is carried out at atemperature of 190° C. with an angular frequency within a range ofω=3.981×10⁻³ to 1.0×10² (rad/sec) to obtain G's (ω) at each ω.Measurement is carried out at three to six points per one digit of thefrequency. The unit is represented by Pa.

[0159] (13) Relation Between the Melt Shear Viscosity and HLMI

[0160] Of the ethylene polymer of the present invention, the relationbetween the shear viscosity [ηe(ω=3.981×10⁻³)] (unit: Pa·sec) at 190° C.with a frequency (ω) of 3.981×10⁻³ rad/sec and HLMI satisfies thefollowing formula (xii):

Log(ηe)≧−0.531×Log(HLMI)+6.35  (xii)

[0161] More preferably it satisfies the following formula (xii-1):

Log(ηe)≧−0.531×Log(HLMI)+6.50  (xii-1)

[0162] Further, ηe (ω=3.981×10⁻³) is preferably at least 0.3 Mpa·sec,more preferably at least 0.6 Mpa·sec, whereby an ethylene polymer havingexcellent elongating property, drawdown resistance, ESCR and impactresistance will be obtained.

[0163] In the condition (13), in order that the relation between ηe andHLMI satisfies the formula (xii), the molecular weight distribution andthe degree of long chain branching are controlled.

[0164] Production Method

[0165] The physical properties of the ethylene polymer of the presentinvention are explained above. Now, a method for producing the ethylenepolymer having the above-described physical properties will be explainedbelow. The periodic law of atoms employed in the present specificationis based on Group XVIII method as recommended by IUPAC in 1989.

[0166] In order to obtain an ethylene polymer which satisfies at leastone condition selected from the conditions (1) to (4), or (1) to (4) and(5) to (13), it is necessary to select the catalyst, the polymerizationcondition and the polymerization process carefully. For example, in acase where a known traditional Ziegler catalyst, traditional Crcatalyst, metallocene catalyst or single site catalyst comprising atransition metal of Group III to XI of the Periodic Table as a centermetal is employed, a conventionally known multistage polymerizationmethod which comprises multistage polymerization steps with differentpolymerization conditions such as the ethylene partial pressure, thehydrogen concentration, the comonomer concentration and the temperature,or a multistage polymerization method which comprises using ametallocene catalyst as disclosed in JP-A-10-245418 may be referred to.

[0167] In a case where a metallocene catalyst is employed, production iscarried out preferably by homopolymerizing ethylene or copolymerizingethylene with an α-olefin such as 1-butene, 1-hexene or 1-octene, in thepresence of a catalyst system containing the following components [A]and [B], and [C] as the case requires.

[0168] [A] A transition metal compound of Group IV to VI of the PeriodicTable having at least one conjugated fivemembered cyclic ligand

[0169] [B] Ion exchangeable layered silicate

[0170] [C] Organic aluminum compound

[0171] Component [A]

[0172] The component [A] used for the catalyst of the present inventionis a transition metal compound of Group IV to VI of the Periodic Tablecontaining at least one conjugated five-membered cyclic ligand.Preferred as the transition metal compound is a compound of thefollowing formula [1], [2], [3] or [4]:

[0173] [wherein each of A and A′ is a ligand having a conjugatedfive-membered cyclic structure (A and A′ may be the same or different inthe same compound), Q is a binding group which crosslinks two conjugatedfive-membered cyclic ligands at an optional position, Z is a ligandcontaining a nitrogen atom, an oxygen atom, a silicon atom, a phosphorusatom or a sulfur atom, or a hydrogen atom, a halogen atom or ahydrocarbon group, which is bonded to M, Q′ is a binding group whichcrosslinks a conjugated five-membered cyclic ligand at an optionalposition and Z, M is a metal atom selected from Groups IV to VI elementsof the Periodic Table, and each of X and Y is a hydrogen atom, a halogenatom, a hydrocarbon group, an alkoxy group, an amino group, aphosphorus-containing hydrocarbon group or a silicon-containinghydrocarbon group, which is bonded to M].

[0174] Each of A and A′ is a conjugated five-membered cyclic ligand, andthey may be the same or different in the same compound, as mentionedabove. As a typical example of the conjugated five-membered cyclicligand (each of A and A′), a conjugated carbon fiver-membered cyclicligand i.e. a cyclopentadienyl group may be mentioned. Thecyclopentadienyl group may be one having five hydrogen atoms [C₆H₅], ormay be its derivative, i.e. one having some of its hydrogen atomssubstituted with substituents. One specific example of the substituentis a hydrocarbon group having a carbon number of from 1 to 20,preferably from 1 to 12, and the hydrocarbon group may be bonded to acyclopentadienyl group as a monovalent group, or in a case where aplurality of the hydrocarbon groups are present, two of them may bebonded at the respective other edges (ω-edges) to form a ring togetherwith a part of the cyclopentadienyl group. The representative example ofthe latter is a condensed six-membered ring formed by two substituentsbonded at the respective ω-edges with two adjacent carbon atoms of thecyclopentadienyl group, i.e. an indenyl group, a fluorenyl group or anazulenyl group.

[0175] Accordingly, the typical example of the conjugated five-memberedcyclic ligand (each of A and A′) is a substituted or non-substitutedcyclopentadienyl group, indenyl group or fluorenyl group.

[0176] As the substituent of the cyclopentadienyl group, in addition tothe above hydrocarbon group having a carbon number of from 1 to 20,preferably from 1 to 12, a halogen group (such as fluorine, chlorine orbromine), an alkoxy group (such as one having a carbon number of from 1to 12), a silicon-containing hydrocarbon group (such as a group having acarbon number at a level of from 1 to 24 and containing a silicon atomin the form of —Si(R¹)(R²)(R³)), a phosphorus-containing hydrocarbongroup (such as a group having a carbon number at a level of from 1 to 18and containing a phosphorus atom in the form of —P(R¹)(R²)), anitrogen-containing hydrocarbon group (such as a group having a carbonnumber at a level of from 1 to 18 and containing a nitrogen atom in theform of —N(R¹) (R²)) or a boron-containing hydrocarbon group (such as agroup having a carbon number at a level of from 1 to 18 and containing aboron atom in the form of —B(R¹)(R²)), may be mentioned. If a pluralityof such substituents is present, these substituents may be the same ordifferent.

[0177] Q is a binding group which crosslinks two conjugatedfive-membered cyclic ligands at an optional position, and Q′ is abinding group which crosslinks a conjugated five-membered cyclic ligandat an optional position and a Z group. Preferred is an alkylene group ora silylene group.

[0178] M is a metal atom selected from Groups IV to VI elements of thePeriodic Table, preferably an atom of Group IV of the Periodic Table,specifically titanium, zirconium or hafnium.

[0179] Z is a ligand containing a nitrogen atom, an oxygen atom, asilicon atom, a phosphorus atom or a sulfur atom, or a hydrogen atom, ahalogen atom or a hydrocarbon group, which is bonded to M.

[0180] Each of X and Y which may be the same or different, is selectedfrom hydrogen, a halogen group and a hydrocarbon group having a carbonnumber of from 1 to 8. Each of them is particularly preferably halogen.

[0181] In the present invention, the component [A] may be a mixture ofat least two compounds among the compound group of the same formula and(or) compounds of the different formulae.

[0182] Specific examples of the transition metal compound wherein M iszirconium are as follows.

[0183] (I) compounds of the formula [1], i.e. transition metal compoundshaving two conjugated five-membered cyclic ligands and having no bindinggroup Q, such as (1) bis(cyclopentadienyl)zirconium dichloride, (2)bis(dimethylcyclopentadienyl)zirconium dichloride, (3)bis(pentamethylcyclopentadienyl)zirconium dichloride, (4)bis(n-butylcyclopentadienyl)zirconium dichloride, (5)bis(n-butyl-methyl-cyclopentadienyl)zirconium dichloride, (6)(cyclopentadienyl)(ethyl-methyl-cyclopentadienyl)zirconium dichloride,(7) (n-butylcyclopentadienyl)(dimethylcyclopentadienyl)zirconiumdichloride, (8) bis(indenyl)zirconium dichloride, (9)bis(tetrahydroindenyl)zirconium dichloride, (10)bis(2methylindenyl)zirconium dichloride, (11) bis(fluorenyl)zirconiumdichloride, (12) bis(cyclopentadienyl)zirconium dimethyl, (13)(cyclopentadienyl)(indenyl)zirconium dichloride, (14)(cyclopentadienyl)(fluorenyl)zirconium dichloride and (15)(cyclopentadienyl)(azulenyl)zirconium dichloride.

[0184] (II) Compounds of the formula [2.], such as (II-1) one whereinthe binding group Q is an alkylene group, such as (1)methylenebis(indenyl)zirconium dichloride, (2)ethylenebis(indenyl)zirconium dichloride, (3)ethylenebis(4,5,6,7-tetrahydroindenyl)zirconium dichloride, (4)ethylenebis(2-methylindenyl)zirconium dichloride, (5)ethylene(2,4-dimethylcyclopentadienyl)(3′,5′-dimethylcyclopentadienyl)zirconiumdichloride, (6) ethylene 1,2-bis[4-(2,7-dimethylindenyl)]zirconiumdichloride, (7) isopropylidenebis(indenyl)zirconium dichloride, (8)methylene(cyclopentadienyl)(3,4-dimethylcyclopentadienyl)zirconiumdichloride, (9)isopropylidene(cyclopentadienyl)(3,4-dimethylcyclopentadienyl)zirconiumdichloride, (10) isopropylidene(cyclopentadienyl)(fluorenyl)zirconiumdichloride, (11)ethylene(cyclopentadienyl)(3,5-dimethylpentadienyl)zirconium dichloride,(12) ethylene(2,5-dimethylcyclopentadienyl)(fluorenyl)zirconiumdichloride, (13)diphenylmethylene(cyclopentadienyl)(3,4-diethylcyclopentadienyl)zirconiumdichloride, (14) cyclohexylidene(cyclopentadienyl)(fluorenyl)zirconiumdichloride and (15)dichloro{1,1′-dimethylmethylenebis[2-methyl-4-(4-biphenyl)-4H-azulenyl]}zirconium.

[0185] (II-2) One wherein Q is a silylene group, such as (1)dimethylsilylenebis(2-methylindenyl)zirconium dichloride, (2)dimethylsilylenebis(2,4-dimethylindenyl)zirconium dichloride, (3)dimethylsilylenebis(2-methyl-4,5,6,7-tetrahydroindenyl)zirconiumdichloride, (4) dimethylsilylenebis(2-methyl-4,5-benzoindenyl)zirconiumdichloride, (5) dimethylsilylenebis(2-methyl-4-phenylindenyl)zirconiumdichloride, (6) dimethylsilylenebis[4-(2-phenylindenyl)]zirconiumdichloride, (7)dimethylsilylenebis[4-(2-phenyl-3-methylindenyl)]zirconium dichloride,(8) phenylmethylsilylenebis(4,5,6,7-tetrahydroindenyl)zirconiumdichloride, (9) phenylmethylsilylene(2,4-dimethylcyclopentadienyl)(3′,5′-dimethylcyclopentadienyl)zirconiumdichloride, (10) diphenylsilylenebis(indenyl)zirconium dichloride, (11)tetramethyldisilylenebis(cyclopentadienyl)zirconium dichloride, (12)dimethylsilylene(cyclopentadienyl) triethylcyclopentadienyl)zirconiumdichloride, (13) dimethylsilylene(cyclopentadienyl)(fluorenyl)zirconiumdichloride, (14) dimethylsilylene(diethylcyclopentadienyl)(octahydrofluorenyl)zirconium dichloride and(15) dimethylsilylenebis[1-(2-methyl-4phenyl-4H-azulenyl]zirconiumdichloride.

[0186] (II-3) One wherein Q is a hydrocarbon group containing germanium,phosphorus, nitrogen, boron or aluminum, such as (1)dimethylgermaniumbis(indenyl)zirconium dichloride, (2)methylaluminumbis(indenyl)zirconium dichloride, (3)phenylphosphinobis(indenyl)zirconium dichloride and (4)phenylamino(cyclopentadienyl)(fluorenyl)zirconium dichloride.

[0187] (III) Compounds of the formula [3], i.e. transition metalcompounds having one conjugated five-membered cyclic ligand and havingno binding group Q′, such as (1)pentamethylcyclopentadienyl-bis(phenyl)aminozirconium dichloride, (2)indenyl-bis(phenyl)amidezirconium dichloride, (3)pentamethylcyclopentadienylbis(trimethylsilyl)aminozirconium dichloride,(4) pentamethylcyclopentadienylphenoxyzirconium dichloride, (5)pentamethylcyclopentadienylzirconium trichloride and (6)cyclopentadienylzirconiumbenzyl dichloride.

[0188] (IV) Compounds of the formula [4], i.e. transition metalcompounds having one conjugated five-membered cyclic ligand crosslinkedby the binding group Q′, such as (1)dimethylsilylene(tetramethylcyclopentadienyl) phenylamidezirconiumdichloride, (2)dimethylsilylene(tetramethylcyclopentadienyl)tert-butylamidezirconiumdichloride, (3) dimethylsilylene(indenyl)cyclohexylamidezirconiumdichloride, (4) dimethylsilylene(tetrahydroindenyl)decylamidezirconiumdichloride, (5) dimethylsilylene(tetrahydroindenyl)((trimethylsilyl)amino)zirconium dichloride and (6)dimethylgermane(tetramethylcyclopentadienyl)(phenyl)amino zirconiumdichloride.

[0189] (V) Further, compounds of the above (I) to (IV), wherein chlorineis replaced with e.g. bromine, iodine, hydride, methyl or phenyl mayalso be used.

[0190] In the above examples, di-substituted products of thecyclopentadienyl ring include 1,2- and 1,3-substituted products, andtri-substituted products include 1,2,3- and 1,2,4-substituted products.

[0191] Further, in the present invention, as the component [A],compounds having zirconium as the center metal of each of the zirconiumcompounds of the above (I) to (V) replaced with titanium, hafnium,vanadium, niobium, chromium, molybdenum, tungsten or the like may alsobe used. Among them, preferred are zirconium compounds, hafniumcompounds and titanium compounds.

[0192] {circle over (2)} Component [B]

[0193] The ion exchangeable layered silicate used as the component [B]in the present invention is a silicate compound having such a crystalstructure that faces constituted by e.g. an ionic bond are parallellyoverlaid one on another with a weak binding power, and wherein containedions are exchangeable with one another.

[0194] As specific examples of the ion exchangeable layered silicate,known layered silicates as disclosed in e.g. “Nendo Kobutsugaku (ClayMineralogy)” Haruo Shirouzu, Asakura Shoten (1995) may be employed, andamong them, a smectite group including montmorillonite, sauconite,beidellite, nontronite, saponite, hectorite, stevensite, bentonite andtaeniolite, a vermiculite group and a mica group are preferred, and amica group and a smectite group are particularly preferred.

[0195] Representative examples of the smectite group generally includemontmorillonite, beidellite, saponite, nontronite, hectorite andsauconite. Commercially available products such as “Benclay SL”(manufactured by MIZUSAWA INDUSTRIAL CHEMICALS, LTD.), “Kunipia” and“Smectone” (each manufactured by Kunimine Industries Co., Ltd.),“montmorillonite K10” (manufactured by Aldrich, manufactured by JuteChemie) and “K-Catalysts series” (manufactured by Jute Chemie) may beutilized.

[0196] Representative examples of the mica group include white mica,palagonite, bronze mica, black mica and lepidolite. Commerciallyavailable products such as “synthetic mica Somasif” (manufactured byCO-OP CHEMICAL CO., LTD.), “fluorine bronze mica”, “fluorotetrasilicicmica” and “taeniolite” (each manufactured by TOPY INDUSTRIES LIMITED)may also be utilized.

[0197] Further, the component [B] is preferably subjected to a chemicaltreatment. As the chemical treatment, either a surface treatment ofremoving impurities attached on the surface or a treatment whichinfluences the crystal structure of the clay may be employed.

[0198] Preferred chemical treatment is a salt treatment and/or acidtreatment. With respect to the catalyst for olefin polymerizationobtained by combination of a layered silicate with a metallocenecomplex, the layered silicate can activate the metallocene complex. Whatis important is that the catalyst may be a multi site catalyst regardingthe polymerization active site, by the structure of the layeredsilicate. Thus, the metallocene catalyst as a single site catalyst in acase where aluminoxane is used functions as a multi site catalyst.Accordingly, a polymer having a conventional molecular weight and apolymer having an ultrahigh molecular weight can be formed in a singlepolymerization. By the acid treatment, metal atoms contained in thelayered silicate can be eluted, whereby specific active sites can beformed. On the other hand, by the salt treatment, cations presentbetween layers can be exchanged, and the distance between layers can bechanged depending upon the size of the cations exchanged, whereby theactive precursor sites in the inside of the silicate can be contactedwith the metallocene complex. By controlling the compound used, thetreatment concentration, the treatment temperature and the like in suchan acid treatment or salt treatment, the structure of the layeredsilicate after the treatment can be controlled.

[0199] In the present invention, it is necessary that at least 30%,preferably at least 40%, particularly preferably at least 60%, of theexchangeable cations contained in at least one compound selected fromthe group consisting of ion exchangeable layered silicates, before thetreatment with a salt, are subjected to ion exchange with cationsdissociated from the following salt. The salt used in the salt treatmentof the present invention with a purpose of such an ion exchange is acompound containing cations containing at least one type of atomsselected from the group consisting of Group II to XIV atoms.

[0200] Such a salt may be used alone or in combination of at least twotypes simultaneously and/or continuously. To produce the ethylenepolymer of the present invention, as the salt employed in the salttreatment, at least one type of a cation selected from the groupconsisting of the Groups IV to VI atoms and at least one type of ananion selected from anions of halogen atoms, inorganic acids and organicacids, is preferred, and among specific examples thereof, particularlypreferred are the above-exemplified salts containing Ti²⁺, Ti³⁺, Ti⁴⁺,Zr²⁺, Zr³⁺, Zr⁴⁺, Hf²⁺, Hf³⁺, Hf⁴⁺, Cr²⁺, Cr³⁺, Cr⁴⁺, Cr⁵⁺ or Cr⁶⁺.Among these specific examples, most preferred are salts containing Cr²⁺,Cr³⁺, Cr⁴⁺, Cr⁵⁺ or Cr⁶⁺.

[0201] By the acid treatment, a part or the whole of the cations of e.g.Al, Fe or Mg in the crystal structure are eluted, in addition to removalof impurities on the surface. The acid used in the acid treatment ispreferably selected from hydrochloric acid, sulfuric acid, nitric acid,acetic acid and oxalic acid. Each of the salt and the acid used for thetreatment may be a combination of at least two types. In a case wherethe salt treatment and the acid treatment are combined, a method ofcarrying out the salt treatment and then carrying out the acidtreatment, a method of carrying out the acid treatment and then carryingout the salt treatment, or a method of carrying out the salt treatmentand the acid treatment at the same time, may be mentioned.

[0202] The conditions of each of the treatments with the salt and theacid are not particularly limited, however, usually the salt or acidconcentration is from 0.1 to 50 wt %, the treatment temperature is fromroom temperature to the boiling point, and the treatment time is from 5minutes to 24 hours, and the treatment is preferably carried out undersuch a condition that at least part of the substance constituting atleast one compound selected from the group consisting of ionexchangeable layered silicates is eluted. Further, the salt and the acidis employed usually as an aqueous solution, but the treatment may becarried out in an organic solvent such as acetone, ethanol, hexane ortoluene depending on the circumstances.

[0203] The component [B] is preferably subjected to a granulation stepfrom the viewpoint of improving the power property of the obtainedpolymer, and particularly preferably atomizing granulation is employed.The timing of the treatment may be either before or after the acidtreatment and/or the salt treatment.

[0204] {circle over (3)} Component [C]

[0205] Further, in the present invention, as examples of an organicaluminum compound used as the component [C] as the case requires, thecompound of the following formula may be mentioned:

AlR⁸ _(j)X_(3-j)

[0206] wherein R⁸ is a hydrocarbon group having a carbon number of from1 to 20, X is hydrogen, halogen or an alkoxy group, and j is a number of0<j≦3.

[0207] Specific examples of the above organic aluminum compound includetrialkylaluminum such as trimethylaluminum, triethylaluminum,tripropylaluminum, triisobutylaluminum and trioctylaluminum, andhalogen- or alkoxy-containing alkyl aluminum such as diethylaluminummonochloride and diethylaluminum methoxide. Among them, trialkylaluminumis preferred, triethylaluminum or triisobutylaluminum is more preferred,and triethylaluminum is most preferred.

[0208] {circle over (4)} Preparation of catalyst

[0209] In the present invention, it is preferred that ethylene iscontacted with the above components [A] and [B] and the component [C]used as the case requires, for preliminary polymerization to obtain acatalyst. As the contact conditions of the component [A], the component[B] and the component [C] as the case requires, a known method may beemployed.

[0210] {circle over (5)} Production of Ethylene Polymer

[0211] The homopolymerization reaction of ethylene or thecopolymerization reaction with another olefin is carried out by usingthe above obtained solid catalyst component, preferably solid catalystcomponent preliminarily polymerized with ethylene. At this time, anorganic aluminum compound may be used as the case requires. The organicaluminum compound used may be the same compound as the compound whichcan be used as the component [C]. As the amount of the organic aluminumcompound, the molar ratio of the transition metal in the catalystcomponent [A] to aluminum in the organic aluminum compound is within arange of 1:0 to 10000. Particularly as the additional condition, theratio of aluminum in the organic aluminum compound to the catalystcomponent [B] is selected to be from 4.0 to 100 mmol-Al/g-[B], wherebythe ethylene polymer of the present invention having the above-describedexcellent physical properties can be obtained with a single catalyst ina single reactor without using a plurality of catalysts in combinationor without a special method such as multistage polymerization.

[0212] The ratio of aluminum in the organic aluminum compound to thecatalyst component [B] is more preferably from 10.0 to 80.0mmol-Al/g-[B], most preferably from 20.0 to 60.0 mmol-Al/g-[B]. Thealuminum concentration in the organic aluminum compound in thepolymerization system is preferably from 0.20 to 5.00 mmol-Al/L-solvent,more preferably from 0.30 to 2.00 mmol-Al/L-solvent, most preferablyfrom 0.40 to 1.00 mmol-Al/L-solvent, in the case of a slurrypolymerization method.

[0213] In the present invention, the Mlmax can be controlled to be adesired value by increasing or decreasing the amount of hydrogen as amolecular weight modifier. On the other hand, as described above, thelayered silicate subjected to a certain chemical treatment can formextremely small hydrogen-responsive sites in actuation of themetallocene complex, and as a result, an ultrahigh molecular weightethylene polymer which is less likely to be influenced by the feedamount of hydrogen can be formed.

[0214] The ethylene polymer of the present invention can be produced byhomopolymerizing ethylene or copolymerizing ethylene with anotherolefin, and it is preferably produced by homopolymerization of ethyleneso as to obtain a polymer having particularly high rigidity among theethylene polymers of the present invention.

[0215] The polymerization reaction is carried out in the presence orabsence of an inert hydrocarbon such as butane, pentane, hexane,heptane, toluene or cyclohexane or a solvent such as liquid α-olefin.The temperature is from −50 to 250° C. and the pressure is notparticularly limited, but is preferably within a range of from normalpressure to about 2000 kgf/cm². Further, hydrogen may be present as amolecular weight modifier in the polymerization system, and it ispreferred as a modifier of the molecular weight, MI and HLMI. Thepreferred amount of hydrogen to obtain the ethylene polymer of thepresent invention having the above-described excellent physicalproperties is from 0.05 to 5.0 mol %, more preferably from 0.1 to 3.0mol %, most preferably from 0.2 to 2.0 mol %, as the molar ratio basedon ethylene in the vapor phase part of the slurry polymerization systemof n-heptane solvent at a polymerization temperature of from 0 to 110°C. for example. Preferred as the polymerization method is a slurrypolymerization method, a vapor phase polymerization method, a highpressure polymerization method or a solution polymerization method. Morepreferred is a slurry polymerization method or a vapor phasepolymerization method, and most preferred is a slurry polymerizationmethod.

[0216] The component having an adequately high melt viscosity tomaintain a low HLMI value and the ultrahigh molecular weight componentare produced preferably by homopolymerizing ethylene or copolymerizingethylene with an α-olefin such as 1-butene, 1-hexene or 1-octene underthe above-described conditions in the presence of the above-describedcatalyst system containing the catalyst components [A] and [B], and [C]as the case requires. At this time, it is important that the ratio ofaluminum in the organic aluminum compound used for the polymerizationreaction to the catalyst component [B] and the aluminum concentration ofthe organic aluminum compound in the polymerization system are withinthe above-described ranges.

[0217] Further, the adequately highly crystalline component to maintaina high density value and the low molecular weight component with anarrow molecular weight distribution to control Mlmax to be within apreferred range, may be produced by the above-described polymerizationmethod in the presence of the above-described catalyst system. At thistime, the polymerization temperature and the molar ratio of hydrogenpresent as the molecular weight modifier in the polymerization system toethylene are important. Further, the crystallinity distribution may becontrolled by appropriately selecting the type and the feed amount ofthe comonomer and the catalyst. In the case of ethylenehomopolymerization, it is controlled by appropriately selecting thecatalyst and by controlling the molecular weight distribution.

[0218] With the ethylene polymer of the present invention, an additivesuch as a weathering stabilizer, a heat-resisting stabilizer, anantistatic agent, a slipping agent, an anti-blocking agent, ananti-fogging agent, a lubricant, a pigment, a crystalline nucleus agent,an anti-aging agent, a hydrochloric acid absorbing agent or anantioxidant may be blended as the case requires within a range of notimpairing the purpose of the present invention.

EXAMPLES

[0219] Now, the present invention will be specifically explained withreference to Examples. However, the present invention is by no meansrestricted to such specific Examples.

[0220] Measuring methods and definitions of the physical property valuesemployed in the present invention are as described above. “%” represents“wt %” unless otherwise specified.

Example 1

[0221] (1) Chemical Treatment and Granulation of Clay Mineral

[0222] 8 kg of commercially available montmorillonite (“Kunipia F”,manufactured by Kunimine Industries Co., Ltd.) was pulverized by avibrating ball mill and dispersed in 50L of demineralized water having10 kg of magnesium chloride dissolved therein, followed by stirring at80° C. for 1 hour. The obtained solid component was washed with water,then dispersed in 56L of a 8.2% hydrochloric acid aqueous solution,followed by stirring at 90° C. for 2 hours and washing withdemineralized water. 4.6 kg of a water slurry liquid of montmorillonitethus chemically treated was adjusted to a solid content concentration of15.2%, and subjected to spray drying by a spray dryer. The shape ofparticles obtained by granulation was spherical shape.

[0223] (2) Chromium Salt Treatment of Clay Mineral

[0224] 80 g of commercially available Cr (NO₃)₃.9H₂O was dissolved in1000 g of pure water, then 200 g of the chemically treatedmontmorillonite granulated particles obtained in (1) were dispersedtherein, followed by stirring at 90° C. for 3 hours. This dispersion wassubjected to filtration and washed with demineralized water until pHbecame 6, then the obtained hydrated solid cake was preliminarily driedat 110° C. for 10 hours to obtain 237.1 g of particulate montmorillonitetreated with chromium salt, the whole part of which had goodflowability. 10.45 g of the preliminarily dried montmorilloniteparticles were further dried under reduced pressure at 200° C. for 2hours to obtain 9.13 g of dry montmorillonite particles.

[0225] (3) Organic Al Treatment of Montmorillonite Treated with ChromiumSalt

[0226] 9.13 g of the montmorillonite particles treated with chromiumsalt obtained in (2) was dispersed in 10.8 ml of n-heptane in a 200 mLflask in an atmosphere of nitrogen to obtain a slurry. Then, 44.0 ml ofa n-heptane solution of triethylaluminum (concentration: 0.622 mol/L)was added thereto at room temperature with stirring. After they werecontacted at room temperature for 1 hour, the supernatant liquid wasdrawn out, and the solid part was washed with n-heptane.

[0227] (4) Catalyst Preparation and Preliminary Polymerization

[0228] In an atmosphere of nitrogen, 700 ml of n-heptane and the entireamount of the solid part obtained in (3) were introduced into a reactorhaving a capacity of 1L equipped with an induction stirrer. 0.7304 mmol(0.2135 g) of bis(cyclopentadienyl)zirconium dichloride as a solution of85.4 ml of n-heptane was added thereto, followed by stirring at 30° C.for 10 minutes. Then, 8.76 mmol (1.00 g) of triethylaluminum was addedthereto, the temperature was raised to 60° C., and then stirring wascontinued further for 10 minutes. While keeping the temperature of thesystem, ethylene gas was introduced at a rate of 0.45 NL/min for 113minutes to carry out preliminary polymerization. The supply of ethylenewas terminated, and the entire content in the reactor was drawn out to a2L flask in an atmosphere of nitrogen. 500 mL of heptane was added tothe reactor to draw out the entire content remaining in the reactor tothe flask. The preliminarily polymerized catalyst slurry transferred tothe flask was left to stand, and about 950 mL of the supernatant liquidwas removed, and then the solvent was removed by drying under reducedpressure with heating at 70° C. As a result, 71.25 g of a preliminarilypolymerized catalyst powder was recovered.

[0229] (5) Polymerization of Ethylene

[0230] Ethylene polymerization was carried out by using thepreliminarily polymerized catalyst of the above (4). Namely, purifiednitrogen was passed through the catalyst at 90° C. for adequate drying,and then in an agitated reactor having a capacity of 200L replaced withethylene gas, 100L of n-heptane and 48.0 mmol of triethylaluminum wereadded at room temperature. After the internal temperature of the reactorwas set to 90° C., a predetermined amount of hydrogen (pressure: 20.5kg/cm², volume: 1090 ml) was introduced, then ethylene gas wasintroduced so that the pressure would be 20 KG. While maintaining theinternal temperature and the pressure, 16.0 g of the preliminarilypolymerized catalyst of the above (4) was added to initiate thepolymerization of ethylene. Ethylene was supplied to always maintain apressure of 20 KG during the polymerization, and the polymerization wascontinued for 5 hours. Hydrogen was added in an appropriate amount everyone hour after initiation of the polymerization. The transition ofhydrogen/ethylene ratio (mol %) at the vapor phase part in the reactorafter initiation of the polymerization every 30 minutes was1.096/0.969/0.802/1.105/0.931/0.881/0.766/0.808/0.713/0.669. As aresult, 1.79 kg of a particulate ethylene homopolymer was obtained.

[0231] To 100 parts by weight of the obtained polyethylene, 0.1 part byweight of IRGANOX 1010 (trade name, manufactured by Ciba SpecialtyChemicals) as a hindered phenol type stabilizer, 0.05 part by weight ofIRGAFOS 168 (trade name, manufactured by Ciba Specialty Chemicals) as aphosphite type stabilizer and 0.1 part by weight of calcium stearatewere added, followed by pelletizing, and the obtained pellets weresubjected to various physical property tests and molding tests. Thebasic physical properties of the polymer are shown in Table 1 (No. 1 toNo. 4).

[0232] Further, in FIG. 1, a GPC curve of the polymer is shown. In thedrawing, the horizontal axis represents the common logarithm of theweight average molecular weight, and the vertical axis represents theelution amount (relative value).

Example 2

[0233] (1) Catalyst Preparation and Preliminary Polymerization

[0234] Catalyst preparation and preliminary polymerization were carriedout in the same manner as in Example 1 (1) to (4), except that 1.601mmol (0.468 g) of bis(cyclopentadienyl)zirconium dichloride was usedbased on 9.15 g of the dry montmorillonite particles treated withchromium salt, and the amount of triethylaluminum used at the time ofpreliminary polymerization was 19.18 mmol (2.19 g). As a result, 79.39 gof a preliminarily polymerized catalyst powder was recovered.

[0235] (2) Polymerization of Ethylene

[0236] Ethylene polymerization was carried out by using thepreliminarily polymerized catalyst of the above (1) in the same manneras in Example 1 (5), except that 80 mmol of triethylaluminum was used,and the polymerization time was 3 hours. The transition of thehydrogen/ethylene ratio (mol %) at the vapor phase part in the reactorfrom initiation of the polymerization every 30 minutes was1.091/0.932/0.221/0.269/0.056/0.329/0.319. As a result, 10.8 kg of aparticulate ethylene homopolymer was obtained.

[0237] To 100 parts by weight of the obtained polyethylene, 0.1 part byweight of IRGANOX 1010 (trade name, manufactured by Ciba SpecialtyChemicals) as a hindered phenol type stabilizer, 0.05 part by weight ofIRGAFOS 168 (trade name, manufactured by Ciba Specialty Chemicals) as aphosphite type stabilizer and 0.1 part by weight of calcium stearatewere added, followed by pelletizing, and the obtained pellets weresubjected to various physical property tests and molding tests. Thebasic physical properties of the polymer are shown in Table 1 (No. 1 toNo. 4) and the GPC curve of the polymer is shown in FIG. 1.

Example 3

[0238] (1) Polymerization of Ethylene

[0239] Ethylene polymerization was carried out by using thepreliminarily polymerized catalyst of Example 2 (1) in the same manneras in Example 2 (2), except that the amount of hydrogen introduced tothe reactor before the polymerization was reduced (pressure: 15.0kg/cm², volume: 1090 ml), and the polymerization time was 5 hours. Thetransition of the hydrogen/ethylene ratio (mol %) at the vapor phasepart in the reactor after initiation of the polymerization every 30minutes was 0.830/0.685/0.418/0.421/0.201/0.463/0.224/0.418/0.210/0.411/0.203. As a result, 9.9 kg of a particulate ethylene homopolymer wasobtained.

[0240] To 100 parts by weight of the obtained polyethylene, 0.1 part byweight of IRGANOX 1010 (trade name, manufactured by Ciba SpecialtyChemicals) as a hindered phenol type stabilizer, 0.05 part by weight ofIRGAFOS 168 (trade name, manufactured by Ciba Specialty Chemicals) as aphosphite type stabilizer and 0.1 part by weight of calcium stearatewere added, followed by pelletizing, and the obtained pellets weresubjected to various physical property tests and molding tests. Thebasic physical properties of the polymer are shown in Table 1 (No. 1 toNo. 4), and the GPC curve of the polymer is shown in FIG. 1.

Example 4

[0241] (1) Magnesium Salt Treatment of Clay Mineral

[0242] 216 g of a commercially available granulated and classifiedproduct of swelling montmorillonite (“Benclay SL”, manufactured byMIZUSAWA INDUSTRIAL CHEMICALS, LTD., average particle size: 27 um) wasdispersed in 1952 g of a sulfuric acid aqueous solution of magnesiumsulfate (magnesium sulfate concentration: 7.18%, sulfuric acidconcentration: 11.8%), followed by stirring at 100° C. for 2 hours. Thedispersion was subjected to filtration and washed with demineralizedwater, and the obtained solid cake was dried at 110° C. for 10 hours toobtain 187 g of preliminarily dried montmorillonite. The preliminarilydried montmorillonite was sieved with a screen having an aperture of 150μm, and the particles passed through the screen were further dried underreduced pressure at 200° C. for 2 hours.

[0243] (2) Chromium Salt Treatment of Clay Mineral

[0244] 24 g of commercially available Cr(NO₃)₃.9H₂O was dissolved in 200g of pure water, and then 10 g of the chemically treated montmorillonitegranulated particles obtained in (1) were dispersed, followed bystirring at 90° C. for 3 hours. The dispersion was subjected tofiltration and washed with demineralized water until pH became 6, andthe obtained hydrated solid cake was preliminarily dried at 110° C. for10 hours to obtain a particulate montmorillonite treated with chromiumsalt, the whole part of which had good flowability. 6.17 g of thepreliminary dried montmorillonite particles were further dried underreduced pressure at 200° C. for 2 hours to obtain 5.85 g of drymontmorillonite particles.

[0245] (3) Organic Al Treatment of Montmorillonite Treated with ChromiumSalt

[0246] In an atmosphere of nitrogen, 5.85 g of the montmorilloniteparticles treated with chromium salt obtained in (2) were dispersed in6.9 ml of n-heptane in a 200 mL flask to obtain a slurry. Then, 28.2 mlof a n-heptane solution of triethylaluminum (concentration: 0.622 mol/L)was added thereto at room temperature with stirring. After they werecontacted at room temperature for 1 hour, the supernatant liquid wasdrawn out, and the solid part was washed with n-heptane.

[0247] (4) Catalyst Preparation and Preliminary Polymerization

[0248] In an atmosphere of nitrogen, 736 ml of n-heptane and the entireamount of the solid part obtained in (3) were introduced into a reactorhaving a capacity of 1L, equipped with an induction stirrer. 0.4680 mmol(0.1368 g) of bis(cyclopentadienyl)zirconium dichloride as a solution of54.7 ml of n-heptane was added thereto, followed by stirring at 30° C.for 10 minutes. Then, 5.61 mmol (0.641 g) of triethylaluminum was addedthereto, the temperature was raised to 60° C., and stirring wascontinued further for 10 minutes. While maintaining the temperature ofthe system, ethylene gas was introduced at a rate of 0.45 NL/min for 100minutes to carry out preliminary polymerization. The supply of ethylenewas terminated, and the entire content in the reactor was drawn out to a2L flask in an atmosphere of nitrogen. 500 mL of heptane was added tothe reactor to draw out the entire content remaining in the reactor tothe flask. The preliminarily polymerized catalyst slurry transferred tothe flask was left to stand, about 950 mL of the supernatant liquid wasremoved, and the solvent was removed by drying under reduced pressurewith heating at 70° C. As a result, 50.76 g of a preliminarilypolymerized catalyst powder was recovered.

[0249] (5) Polymerization of Ethylene

[0250] Ethylene polymerization was carried out by using thepreliminarily polymerized catalyst of the above (4) in the same manneras in Example 1 (5), except that the amount of triethylaluminum was 80.0mmol, and the polymerization time was 5 hours. The transition of thehydrogen/ethylene ratio (mol %) at the vapor phase part in the reactor,from one hour after the initiation of the polymerization every 30minutes, was 0.476/0.543/0.361/0.405/0.267/0.403/0.264/0.341/0.249. As aresult, 4.2 kg of a particulate ethylene homopolymer was obtained.

[0251] To 100 parts by weight of the obtained polyethylene, 0.1 part byweight of IRGANOX 1010 (trade name, manufactured by Ciba SpecialtyChemicals) as a hindered phenol type stabilizer, 0.05 part by weight ofIRGAFOS 168 (trade name, manufactured by Ciba Specialty Chemicals) as aphosphite type stabilizer and 0.1 part by weight of calcium stearatewere added, followed by pelletizing, and the obtained pellets weresubjected to various physical property tests and molding tests. Thebasic physical properties of the polymer are shown in Table 1 (No. 1 toNo. 4) and the GPC curve of the polymer is shown in FIG. 1.

Comparative Example 1

[0252] (1) Chromium Salt Treatment of Clay Mineral

[0253] 20 g of the chemically treated montmorillonite granulatedparticles obtained in Example 1 (1) were weighed in a 1L flask, and thendispersed in 400 ml of demineralized water having 48 g of commerciallyavailable Cr(NO₃)₃.9H₂O dissolved therein, followed by stirring at 90°C. for 3 hours. After the treatment, the solid component was washed withdemineralized water and dried to obtain chemically treatedmontmorillonite. 10.0 g of the preliminarily dried montmorilloniteparticles were further dried under reduced pressure at 200° C. for 2hours to obtain 8.7 g of dry montmorillonite particles.

[0254] (2) Organic Al Treatment of Montmorillonite Treated with ChromiumSalt

[0255] In an atmosphere of nitrogen, 3.0 g of the montmorilloniteparticles treated with chromium salt obtained in (1) was put in a 100 mLflask, and dispersed in 20 ml of toluene to obtain a slurry. Then, 1.3ml of triethylaluminum was added at room temperature with stirring.After they were contacted at room temperature for 1 hour, thesupernatant liquid was drawn out, and the solid part was washed withtoluene.

[0256] (3) Preparation of Catalyst

[0257] Subsequently to (2), in an atmosphere of nitrogen, toluene wasadded to obtain a slurry, and 12.0 ml of a toluene solution ofbis(cyclopentadienyl)zirconium dichloride (20.0 μmol/ml) was addedthereto, followed by stirring at room temperature for 1 hour to obtain acatalyst component.

[0258] (4) Polymerization of Ethylene

[0259] Into a 2L induction stirrer type autoclave adequately replacedwith purified nitrogen, 1L of n-hexane, 0.15 mmol of triethylaluminumand 100.0 mg of the catalyst component obtained in (3) were introduced.Then, the temperature was raised to 90° C., ethylene was introduced tomaintain the total pressure at 22.0 kgf/cm², and stirring was continuedto carry out polymerization for 1 hour. The polymerization wasterminated by addition of 10 ml of ethanol. The amount of the obtainedethylene polymer was 280 g.

[0260] To 100 parts by weight of the obtained polyethylene, 0.1 part byweight of IRGANOX 1010 (trade name, manufactured by Ciba SpecialtyChemicals) as a hindered phenol type stabilizer, 0.05 part by weight ofIRGAFOS 168 (trade name, manufactured by Ciba Specialty Chemicals) as aphosphite type stabilizer and 0.1 part by weight of calcium stearatewere added, followed by pelletizing, and the obtained pellets weresubjected to various physical property tests and molding tests. Thebasic physical properties of the polymer are show in Table 1 (No. 1 toNo. 4).

Comparative Example 2

[0261] (1) Polymerization of Ethylene

[0262] Polymerization of ethylene was carried out in the same manner asin Comparative Example 1 (5) except that the amount of the catalystcomponent obtained in Comparative Example 1 (4) was 120 mg, and hydrogenwas added so that the gas composition in the autoclave would be[hydrogen/ethylene]=0.034 mol %. The amount of the obtained ethylenepolymer was 310 g.

[0263] To 100 parts by weight of the obtained polyethylene, 0.1 part byweight of IRGANOX 1010 (trade name, manufactured by Ciba SpecialtyChemicals) as a hindered phenol type stabilizer, 0.05 part by weight ofIRGAFOS 168 (trade name, manufactured by Ciba Specialty Chemicals) as aphosphite type stabilizer and 0.1 part by weight of calcium stearatewere added, followed by pelletizing, and the obtained pellets weresubjected to various physical property tests and molding tests. Thebasic physical properties of the polymer are shown in Table 1 (No. 1 toNo. 4).

Comparative Example 3

[0264] (1) Chromium Salt Treatment of Clay Mineral

[0265] 20 g of the chemically treated montmorillonite granulatedparticles obtained in Example 1 (1) were weighed in a 1L flask, and thendispersed in 400 ml of demineralized water having 48 g of commerciallyavailable Cr(NO₃)₃.9H₂O dissolved therein, followed by stirring at 90°C. for 3 hours. After the treatment, the solid component was washed withdemineralized water and dried to obtain chemically treatedmontmorillonite. 10.0 g of the preliminarily dried montmorilloniteparticles were further dried under reduced pressure at 200° C. for 2hours to obtain 8.7 g of dry montmorillonite particles.

[0266] (2) Organic Al Treatment of Montmorillonite Treated with ChromiumSalt

[0267] In an atmosphere of nitrogen, 3.0 g of the montmorilloniteparticles treated with chromium salt obtained in (1) was put in a 100 mLflask, and dispersed in 20 ml of toluene to obtain a slurry. Then, 1.3ml of triethylaluminum was added thereto at room temperature withstirring. After they were contacted at room temperature for 1 hour, thesupernatant liquid was drawn out, and the solid part was washed withtoluene.

[0268] (3) Catalyst Preparation

[0269] Subsequently to (2), in an atmosphere of nitrogen, toluene wasadded to obtain a slurry, and 12.0 ml of a toluene solution ofbis(cyclopentadienyl)zirconium dichloride (20.0 umol/ml) was addedthereto, followed by stirring at room temperature for 1 hour to obtain acatalyst component.

[0270] (4) Polymerization of Ethylene

[0271] Into a 2L induction stirrer type autoclave adequately replacedwith purified nitrogen, 1L of nhexane, 0.15 mmol of triethylaluminum and120 mg of the catalyst component obtained in (3) were introduced. Then,the temperature was raised to 90° C., and hydrogen was added so that thegas composition in the autoclave would be [hydrogen/ethylene]=0.034 mol%, and then ethylene was introduced to maintain the total pressure at22.0 kgf/cm², and stirring was continued to carry out the polymerizationfor 1 hour. The polymerization was terminated by addition of 10 ml ofethanol. The amount of the obtained ethylene polymer was 310 g. Thebasic physical properties of the polymer are shown in Table 1 (No. 1 toNo. 4).

Comparative Example 4

[0272] (1) Preparation of Solid Catalyst Component

[0273] A catalyst component was prepared by using a complex as disclosedin Examples of JP-A-9-328520, which is reputed an ethylene polymerexcellent in moldability. Namely, 6.0 g of commercially availablesilica-supported methylaluminoxane (manufactured by Witco, TA02794,containing 50 wt % as methylaluminoxane) was slurryed with 50 ml oftoluene, and 11.1 ml of a toluene solution ofdimethylsilylenebis(3-methylcyclopentadienyl)zirconium dichloride(mixture ratio with a diastereoisomer of 1:1) (Zr=0.0103 mmol/ml) wasdropwise added thereto at 20° C. over a period of 30 minutes. Then, thetemperature was raised to 80° C., and the reaction was carried out atthe temperature for 2 hours. Then, the supernatant liquid was removed,followed by washing with heptane twice.

[0274] (2) Preliminary Polymerization of Ethylene

[0275] 4 g of the solid catalyst obtained in the above (1) was slurryedagain with 200 ml of heptane. 6.84 ml of a heptane solution oftriisobutylaluminum (0.731 mmol/ml) and 0.36 g of 1-hexene were addedthereto to carry out preliminary polymerization of ethylene at 35° C.,whereby 3 g of polyethylene was preliminarily polymerized.

[0276] (3) Polymerization of Ethylene

[0277] Into an autoclave made of stainless steel having an internalvolume of 3L adequately replaced with nitrogen, 1.5L of heptane wasintroduced, and the system in the autoclave was replaced with mixed gasof ethylene and hydrogen (hydrogen content: 0.05 mol %). Then, thetemperature in the system was set at 60° C., and 1.5 mmol oftriisobutylaluminum and 180 mg of the preliminarily polymerized catalystprepared in the above (2) were added thereto. Then, mixed gas ofethylene and hydrogen having the same composition as mentioned above wasintroduced, and the polymerization was initiated at a total pressure of8 kg/cm-G. Then, the mixed gas alone was resupplied to maintain thetotal pressure at 8 kg/cm²-G, and polymerization was carried out at 70°C. for 1.5 hours. The results are shown in Table 1 (No. 1 to No. 4).

INDUSTRIAL APPLICABILITY

[0278] The present invention provides an ethylene polymer excellent inmolding processability represented by uniform extensibility, drawdownresistance, swell and extrudability, and mechanical propertiesrepresented by rigidity, impact resistance and ESCR. Particularly, theethylene polymer of the present invention is remarkably excellent inbalance between rigidity and ESCR as compared with a conventionallyknown ethylene polymer. TABLE 1 (No. 1) Fulfill- Fulfill- Flexural mentment mod- of of HLMI Density ulus ESCR formula formula g/10 min g/cm³kgf/cm² hr (i) (ii) Example 1 3.5 0.963 17500 950 ◯ ◯ Example 2 7.50.963 15100 400 ◯ ◯ Example 3 4.2 0.962 14100 950 ◯ ◯ Example 4 17.00.967 18200 740 ◯ ◯ Comparative 0.55 0.946 9500 350 X X Example 1Comparative 4.79 0.954 12000 110 X X Example 2 Comparative 4.51 0.95310200 100 X X Example 3 Comparative 92 0.960 14300 60 X X Example 4

[0279] TABLE 1 (No 2) Heat quantity Melting of HLMI Density point fusionFulfillment Fulfillment g/10 d Mn Mw Q Mlmax Tm ΔH of formula of formulamin g/cm³ (GPC) (GPC) (GPC) (GPC) ° C. J/g (iii) (iv) Example 1 3.50.963 9,130 310,900 34.0 4,591 136.0 226.1 ◯ ◯ Example 2 7.5 0.96313,000 275,600 21.2 12,100 136.8 231.8 ◯ ◯ Example 3 4.2 0.962 13,400324,900 24.2 9,129 135.7 230.0 ◯ ◯ Example 4 17.0 0.967 10,500 227,80021.7 7,916 135.0 241.3 ◯ ◯ Comparative 0.55 0.946 192,100 707,200 3.7317,000 — — X — Example 1 Comparative 4.79 0.954 99,200 572,100 5.8163,100 — — X — Example 2 Comparative 4.51 0.953 109,300 591,400 5.4191,300 135.4 209.4 X X Example 3

[0280] TABLE 1 (No. 3) Mw Mc value Swell (Malls) (%) R Lm ratio MTExample 1 521,000 15.2 39 1.02 1.45 18.7 Example 2 411,000 13.1 17 1.111.53 9.2 Example 3 457,000 15.2 17 1.05 1.33 9.2 Example 4 384,000 12.317 1.18 1.56 8.6 Comparative 829,100 10.1 24 1.21 1.62 65.1 Example 1Comparative 614,800 8.7 19 1.51 1.91 33.5 Example 2 Comparative 691,4008.7 21 1.49 1.88 18.1 Example 3 Comparative — — 1 >3 1.90 0.9 Example 4

[0281] TABLE 1 (No. 4) G′ (0.1) G′ (1) G′ (10) ηe Pa Pa Pa Pa.s Example1 3.34E+04 9.67E+04 1.52E+05 2.80E+06 Example 2 2.64E+04 5.26E+041.11E+05 1.97E+06 Example 3 3.16E+04 5.77E+04 1.34E+05 2.17E+06 Example4 1.85E+04 4.71E+04 8.62E+04 1.21E+06 Comparative 2.26E+04 3.81E+041.38E+05 1.07E+05 Example 1 Comparative 8.81E+03 2.22E+04 6.49E+048.79E+05 Example 2 Comparative 9.13E+03 2.77E+04 7.81E+04 9.56E+05Example 3 Comparative 4.50E+01 6.21E+02 1.01E+04 5.67E+04 Example 4

1. An ethylene polymer, which is an ethylene homopolymer or a copolymerof ethylene with an α-olefin having a carbon number of from 3 to 20, andwhich satisfies the following conditions (1) to (4): (1) the melt index(HLMI) under a load of 21.6 kg at 190° C. is from 0.1 to 1,000 g/10 min,(2) the density (d) is from 0.935 to 0.985 g/cm³, (3) the relationbetween HLMI and (d) satisfies the following formula (i):d≧0.00900×Log(HLMI)+0.951  (i) (4) the relation between theenvironmental stress cracking resistance (ESCR) and the flexural modulus(M) satisfies the following formula (ii): M≧−7310×Log(ESCR)+32300  (ii)2. The ethylene polymer according to claim 1, wherein the melt index(HLMI) under a load of 21.6 kg at 190° C. of the above condition (1) isfrom 1 to 100 g/10 min.
 3. The ethylene polymer according to claim 1 or2, wherein the relation between HLMI and (d) of the condition (3)satisfies the following formula (i-1): d≧0.00697×Log(HLMI)+0.956  (i-1)4. The ethylene polymer according to any one of claims 1 to 3, whereinthe flexural modulus (M) is at least 15000 kgf/cm².
 5. The ethylenepolymer according to any one of claims 1 to 4, wherein the environmentalstress cracking resistance (ESCR) is at least 500 hours.
 6. The ethylenepolymer according to any one of claims 1 to 5, which satisfies thefollowing conditions (5) and (6) in addition to the conditions (1) to(4): (5) the molecular weight (Mlmax) at the highest peak position inthe molecular weight distribution curve as measured by gel permeationchromatography (GPC) satisfies the relation of the following formula(iii): Log(M1max)≦−0.307×Log(HLMI)+4.87  (iii) (6) the melting point(Tm) as measured by differential scanning calorimetry (DSC) and (d)satisfy the following formula (iv): Tm≦538d−378  (iv)
 7. The ethylenepolymer according to any one of claims 1 to 6, which satisfies thefollowing condition (7) in addition to the conditions (1) to (4): (7) inchromatogram employing a Rayleigh ratio having a scattering angleextrapolated to 0° as obtained by GPCMalls measurement, the areapercentage (Mc value) of the chromatogram of a component having amolecular weight as calculated from this measurement of at least1,000,000 is at least 5%.
 8. The ethylene polymer according to any oneof claims 1 to 7, wherein the ratio (Mw/Mn) of the number averagemolecular weight (Mn) to the weight average molecular weight (Mw) asmeasured by GPC is higher than 7, in addition to the conditions (1) to(4).
 9. The ethylene polymer according to any one of claims 1 to 8,which is obtained by homopolymerization of ethylene or copolymerizationof ethylene with an α-olefin having a carbon number of from 3 to 20, inthe presence of a catalyst containing [A] a transition metal compound ofGroup IV to VI of the Periodic Table having at least one conjugatedfive-membered cyclic ligand and [B] an ion exchangeable layeredsilicate, in a single polymerization apparatus, wherein an organicaluminum compound is used in such an amount that the ratio of aluminumin the organic aluminum compound to the component [B] is within a rangeof from 4.0 to 100 (mmol-Al/g-[B]).
 10. A molded product of an ethylenepolymer, which is obtained by subjecting the ethylene polymer as definedin any one of claims 1 to 9 to injection molding, compression injectionmolding, rotational molding, extrusion, blow molding or blow molding.11. A method for producing the ethylene polymer as defined in any one ofclaims 1 to 8, which comprises homopolymerizing ethylene orcopolymerizing ethylene with an α-olefin having a carbon number of from3 to 20, in the presence of a catalyst containing [A] a transition metalcompound of Group IV to VI of the Periodic Table having at least oneconjugated fine-membered cyclic ligand and [B] an ion exchangeablelayered silicate, in a single polymerization apparatus, wherein anorganic aluminum compound is used in such an amount that the ratio ofaluminum in the organic aluminum compound to the component [B] is withina range of from 4.0 to 100 (mmol-Al/g-[B]).